1. Field of the Invention
The present invention relates to a cylinder type secondary battery.
2. Description of the Related Art
In recent times, compact and lightweight mobile electronic/electric appliances such as cellular phones, notebook computers, camcorders, etc., are being rapidly developed and produced. In order to be able to operate the mobile electronic/electric appliances where there is no separate power source, secondary batteries are used. Such secondary batteries can be repeatedly used by charging and discharging, unlike disposable batteries, which cannot be recharged.
In addition, since secondary batteries have large capacities, they are also used for high-output products such as hybrid automobiles, power tools, etc., in addition to the mobile electronic/electric appliances.
Such secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries, lithium ion secondary batteries, lithium polymer secondary batteries, etc. Among these, lithium secondary batteries are widely used due to their high operation voltage and energy density per unit weight.
Lithium secondary batteries are formed by housing an electrode assembly and electrolyte in an outer case, and then sealing the outer case. Lithium secondary batteries may be classified into a can type battery and a pouch type battery depending on a shape of the outer case, and the can type battery may be further classified as a cylinder type battery or a prismatic type battery.
A cylinder type secondary battery is formed by winding a positive electrode plate, a separator, and a negative electrode plate to form an electrode assembly, housing the electrode assembly and electrolyte in a cylindrical can, and sealing the cylindrical can with a cap assembly.
Uncoated portions on which positive or negative electrode active materials are not applied are on the positive and negative electrode plates of the electrode assembly. Electrode tabs are installed on the uncoated portions of the electrode plates, respectively. One of the electrode tabs extends upward toward the opening of the cylindrical can, and the other extends downward.
In addition, the electrode tab led upward is electrically connected to the cap assembly, and the electrode tab led downward is electrically connected to the bottom of the can.
However, since the electrode tab electrically connected to the cap assembly is bent and welded to the cap assembly such that stress is concentrated on the bent portion of the electrode tab, the electrode tab may be easily detached.